Nitinol and similar shape memory materials (SMM) have unique material properties, which allow them to be pre-formed in a desired “memorized” shape and return to that shape after any deformation above a material specific phase-change temperature. When a heat source is removed and the temperature drops below the phase-change temperature, the shape memory material retains a deformable state. The temperature range for controlling the shape can be varied based on the composition of the SMM and the techniques used to process and form the SMM. Due to the ability to control the shape of such a flexible, yet strong material has led to a variety of applicable uses for SMM.
However, the traditional methods for constructing and controlling a SMM, or actuators that are embedded with SMMs, has been limited for several reasons. SMMs are slow to reach the disparate temperatures required for transition without outside intervention, which typically requires cooling the material after being driven to the opposite phase to allow for transition. To obtain the required temperature range, the materials are generally constructed with individual shape memory elements in much the same way a traditional component such as a wire wound resistor might be, at its ends. However, these constructions lead to very limiting geometries and complex multipart mountings. Furthermore, the constant flexing of the SMM causes the mechanical connections between individual SMM elements to fatigue and rapidly fail overtime, which reduces the overall durability and longevity of these actuators, greatly increasing replacement and maintenance costs.
In addition, traditional methods to control multiple mechanical axis and multiple degrees of freedom of the actuators with SMMs have resorted to using individual conductors to heat each individual SMM element. The more SMM elements to drive the actuator, the more wiring that is required, which results in a larger size actuator, higher costs, reduced durability, and can lead to undesired thermal management design considerations. As such, the current actuators and designs have resulted in poor performance and their control has been limited to only one or two degrees of freedom. Having only one to two degrees of freedom of control greatly limits the use of SMM for a variety of applications.
Thus there is a need in the art for a controllable SMM that greatly reduces or eliminates the need for individual SMM elements. There is a further need to control an actuator or SMM in multiple axes and in multiple degrees of freedom to greatly expand their applicable uses.